Display panel

ABSTRACT

A display panel is provided. The display panel includes a display area comprising a gate line and a data line, and a gate driver connected to a terminal of the gate line. The gate driver includes a plurality of stages that are integrated on a substrate, and each stage comprises an inverter unit, an output unit, and a Q node stabilization unit. The output unit includes a first transistor and a first capacitor, wherein the first transistor includes an input terminal for receiving a clock signal, a control terminal connected to a node Q and an output terminal connected to a gate voltage output terminal to output a gate voltage. A Vgs voltage of a transistor in the Q node stabilization unit has a value of equal to or less than 0 V when the output unit outputs a gate-on voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/203,272 filed Mar. 10, 2014, which claims priority 35 U.S.C. §119 toKorean Patent Application No. 10-2013-0026849 filed in the KoreanIntellectual Property Office on Mar. 13, 2013, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

(a) Field

The present disclosure relates to a display panel, and moreparticularly, a display panel having a gate driver integrated therein.

(b) Description of the Related Art

Liquid crystal panels are widely used in flat display panels. A liquidcrystal panel typically includes two display panels on which fieldgenerating electrodes (such as pixel electrodes and a common electrode)are formed, and a liquid crystal layer interposed between the twodisplay panels. In the liquid crystal display panel, a voltage isapplied to the field generating electrodes so as to form an electricfield in the liquid crystal layer. The electric field influences thealignment of liquid crystal molecules in the liquid crystal layer. Bymanipulating the electric field to control the polarization of incidentlight through the liquid crystal layer, images can be displayed on theliquid crystal panel.

The liquid crystal panel may further include a gate driver and a datadriver. The gate driver may be patterned along with the gate line anddata line, and integrated on the panel using thin film transistors. Byintegrating the gate driver on the panel, savings in manufacturing costscan be realized since an additional (discrete) gate driving chip is notrequired.

However, in some instances, the thin film transistors in the integratedgate driver may generate a leakage current that can cause the gate-offsignal and the gate voltage level to deteriorate.

SUMMARY

The present disclosure addresses at least the above problems relating toleakage current in an integrated gate driver.

According to some embodiments of the inventive concept, a display panelis provided. The display panel includes a display area comprising a gateline and a data line, and a gate driver connected to a terminal of thegate line. The gate driver includes a plurality of stages that areintegrated on a substrate, and at least one of the stages includes aninverter unit, an output unit, and a carry signal generator. The outputunit includes a first transistor and a first capacitor. The firsttransistor includes an input terminal for receiving a clock signal, acontrol terminal connected to a node Q, and an output terminal connectedto a gate voltage output terminal to output a gate voltage at a firstlow voltage. The inverter unit is configured to output voltage at asecond low voltage. The carry signal generator is configured to generatea carry signal at a third low voltage, wherein the second low voltagehas a lower voltage level than the first low voltage, and the third lowvoltage has a lower voltage level than the second low voltage.

In some embodiments, each stage may further include a Q nodestabilization unit, and a Vgs voltage of a transistor in the Q nodestabilization unit may have a value of equal to or less than 0 V whenthe output unit outputs a gate-on voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a sixthtransistor comprising a control terminal for receiving a carry signal ofa second next stage through a third input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the secondlow voltage; a ninth transistor comprising a control terminal forreceiving a carry signal of a next stage through a second inputterminal, an input terminal connected to the node Q, and an outputterminal for receiving the second low voltage; and a tenth transistorcomprising a control terminal connected to a node I wherein the node Icorresponds to an output of the inverter unit, an input terminalconnected to the node Q and an output terminal for receiving the secondlow voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a sixthtransistor comprising a control terminal for receiving a carry signal ofa second next stage through a third input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the thirdlow voltage; a ninth transistor comprising a control terminal forreceiving a carry signal of a next stage through a second inputterminal, an input terminal connected to the node Q, and an outputterminal for receiving the third low voltage; and a tenth transistorcomprising a control terminal connected to a node I wherein the node Icorresponds to an output of the inverter unit, an input terminalconnected to the node Q and an output terminal for receiving the secondlow voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a sixthtransistor comprising a control terminal for receiving a carry signal ofa second next stage through a third input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the secondlow voltage; a ninth transistor comprising a control terminal forreceiving the second low voltage, an input terminal connected to thenode Q and an output terminal for receiving the third low voltage; and atenth transistor comprising a control terminal connected to a node Iwherein the node I corresponds to an output of the inverter unit, aninput terminal connected to the node Q and an output terminal forreceiving the second low voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a ninthtransistor and a ninth-1 transistor comprising a pair of transistorswherein an input terminal of the ninth-1 transistor and an outputterminal of the ninth transistor are connected to each other, controlterminals of the pair of transistors are connected to a second inputterminal for receiving the carry signal of the next stage through thesecond input terminal, an input terminal of the ninth transistor isconnected to the node Q, and an output terminal of the ninth-1transistor for receiving the second low voltage; and a tenth transistorand a tenth-1 transistor comprising a pair of transistors wherein aninput terminal of the tenth-1 transistor and an output terminal of thetenth transistor are connected to each other, control terminals of thepair of transistors are connected to a node I wherein the node Icorresponds to an output of the inverter unit, an input terminal of thetenth transistor is connected to the node Q, and an output terminal ofthe tenth-1 transistor for receiving the second low voltage.

In some embodiments, a fifth transistor may include an input terminalconnected to a node I wherein the node I corresponds to an output of theinverter unit, a control terminal for receiving a carry signal of aprevious stage through a first input terminal, and an output terminalfor receiving the second low voltage.

In some embodiments, the pull-down unit may include a second transistorand a third transistor for decreasing a voltage of the output terminalof the first transistor of the output unit to the first low voltage.

In some embodiments, the pull-down unit may include an eleventhtransistor for decreasing a voltage of the carry signal to the third lowvoltage, and the eleventh transistor may include a control terminalconnected to a node I wherein the node I corresponds to an output of theinverter unit, an input terminal connected to an output terminal of thecarry signal generator, and an output terminal for receiving the thirdlow voltage.

In some embodiments, the pull-down unit may include a seventeenthtransistor for decreasing a voltage of the carry signal to the third lowvoltage, and the seventeenth transistor may include a control terminalfor receiving the carry signal of the next stage through the secondinput terminal, an input terminal connected to the output terminal ofthe carry signal generator, and an output terminal for receiving thethird low voltage.

In some embodiments, the pull-down unit may further include aneleventh-1 transistor for decreasing the gate voltage to the first lowvoltage, and the eleventh-1 transistor may include a control terminalfor receiving an output signal of an inverter of a previous stage, aninput terminal connected to the output terminal of the first transistorof the output unit, and an output terminal for receiving the first lowvoltage.

In some embodiments, the pull-down unit may further include an eleventhtransistor for decreasing a voltage of the carry signal to the secondlow voltage, and the eleventh transistor may include a control terminalconnected to a node I wherein the node I corresponds to the output ofthe inverter unit, an input terminal connected to the output terminal ofthe carry signal generator, and an output terminal for receiving thesecond low voltage.

In some embodiments, the pull-down unit may further include an eleventhtransistor for decreasing a voltage of the carry signal to the first lowvoltage, and the eleventh transistor may include a control terminalconnected to a node I wherein the node I corresponds to the output ofthe inverter unit, an input terminal connected to the output terminal ofthe carry signal generator, and an output terminal for receiving thefirst low voltage.

In some embodiments, a channel of the transistors may include an oxidesemiconductor or an amorphous semiconductor, and when a voltage appliedto each stage is more than −10 V, either the amorphous semiconductor orthe oxide semiconductor may be used to form the channel of thetransistors, and when the voltage applied to each stage is less than −10V, the oxide semiconductor may be used to form the channel of thetransistors.

According to some other embodiments of the inventive concept, a displaypanel is provided. The display panel includes a display area comprisinga gate line and a data line, and a gate driver connected to a terminalof the gate line. The gate driver includes a plurality of stages thatare integrated on a substrate, and each stage comprises an inverterunit, an output unit, and a Q node stabilization unit. The output unitincludes a first transistor and a first capacitor, wherein the firsttransistor includes an input terminal for receiving a clock signal, acontrol terminal connected to a node Q, and an output terminal connectedto a gate voltage output terminal to output a gate voltage. A Vgsvoltage of a transistor in the Q node stabilization unit has a value ofequal to or less than 0 V when the output unit outputs a gate-onvoltage.

In some embodiments, a channel of the first transistor may include anoxide semiconductor or an amorphous semiconductor, and when a voltageapplied to each stage is more than −10 V, either the amorphoussemiconductor or the oxide semiconductor may be used to form the channelof the first transistor, and when the voltage applied to each stage isless than −10 V, the oxide semiconductor may be used to form the channelof the first transistor.

In some embodiments, the output unit may be configured to output thegate voltage at a first low voltage, and the inverter unit may beconfigured to output voltage at a second low voltage, wherein the secondlow voltage has a lower voltage level than the first low voltage.

In some embodiments, each stage may further include a carry signalgenerator configured to generate and output a carry signal at a thirdlow voltage, wherein the third low voltage has a lower voltage levelthan the second low voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a sixthtransistor comprising a control terminal for receiving a carry signal ofa second next stage through a third input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the secondlow voltage; a ninth transistor comprising a control terminal forreceiving a carry signal of a next stage through a second inputterminal, an input terminal connected to the node Q, and an outputterminal for receiving the second low voltage; and a tenth transistorcomprising a control terminal connected to a node I wherein the node Icorresponds to an output of the inverter unit, an input terminalconnected to the node Q and an output terminal for receiving the secondlow voltage.

In some embodiments, the Q node stabilization unit may include a fourthtransistor comprising an input terminal and a control terminal forreceiving a carry signal of a previous stage through a first inputterminal, and an output terminal connected to the node Q; a sixthtransistor comprising a control terminal for receiving a carry signal ofa second next stage through a third input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the thirdlow voltage; a ninth transistor comprising a control terminal forreceiving a carry signal of a next stage through a second inputterminal, an input terminal connected to the node Q, and an outputterminal for receiving the third low voltage; and a tenth transistorcomprising a control terminal connected to a node I as an output of theinverter unit, an input terminal connected to the node Q and an outputterminal for receiving the second low voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a display panel according to an exemplaryembodiment of the inventive concept.

FIG. 2 is a block diagram of the gate driver and gate lines of FIG. 1.

FIG. 3 is a circuit diagram of a stage in a gate driver according to anexemplary embodiment of the inventive concept.

FIG. 4 depicts I-V (current-voltage) curves for a transistor includingan amorphous silicon semiconductor and a transistor including an oxidesemiconductor.

FIG. 5 is a view of the area occupied by a gate driver according to anexemplary embodiment of the inventive concept.

FIG. 6 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment of the inventive concept.

FIGS. 7 and 8 are tables showing the output characteristics of exemplarygate drivers under different operating conditions.

FIGS. 9, 10, 11, 12, 13, 14, 15, 16 and 17 are circuit diagrams of astage in a gate driver according to different embodiments of theinventive concept.

DETAILED DESCRIPTION

The inventive concept will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. As those skilled in the art would realize, the embodimentsmay be modified in various ways without departing from the spirit orscope of the present disclosure.

In the drawings, the thickness of layers, films, panels, regions, etc.,may be exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is described asbeing “on” another element, the element may be disposed on the otherelement with or without any intervening element(s). In contrast, when anelement is described as being “directly on” another element, there areno intervening elements present.

First, a display panel according to an exemplary embodiment of theinventive concept will be described with reference to FIG. 1.

FIG. 1 is a top plan view of an exemplary display panel.

Referring to FIG. 1, a display panel 100 includes a display area 300 fordisplaying images. The display area 300 includes a plurality of gatelines G1-Gn and a plurality of data lines D1-Dm. The plurality of gatelines G1-Gn and the plurality of data lines D1-Dm intersect each other,and are insulated from each other by one or more intervening dielectriclayers.

The display panel 100 also includes a gate driver 500 and a data driverIC 460. The gate driver 500 is configured to apply a gate voltage to agate line of the display area 300. The data driver IC 460 is configuredto apply a data voltage to a data line of the display area 300. In someembodiments, the data driver IC 460 may be formed on a film (e.g., aflexible printed circuit (FPC) film 450) that is attached to the displaypanel 100, as shown in FIG. 1.

The gate driver 500 and the data driver IC 460 are controlled by asignal controller 600. In some embodiments, the signal controller 600 isprovided as a discrete external unit. In some embodiments, the signalcontroller 600 may be formed on a printed circuit board (PCB) 400. Whenthe flexible printed circuit film (FPC) 450 is connected to the printedcircuit board (PCB) 400, signals from the signal controller 600 can betransmitted to the data driver IC 460 and the gate driver 500. Thesignals transmitted from the signal controller 600 may include a firstclock signal CKV, a second clock signal CKVB, a scan start signal STVP,and a signal providing low voltages Vss1, Vss2, and Vss3 of apredetermined voltage level. In an exemplary embodiment, the lowvoltages may include three or more different voltage levels.

In the example of FIG. 1, the display area 300 constitutes part of aliquid crystal panel. It should be noted that the inventive concept isnot limited to a liquid crystal panel. For example, in some otherembodiments, an exemplary display panel may include an organic lightemitting panel, a plasma display panel, or an electrophoretic displaypanel. In those other embodiments, a display area 300 for an organiclight emitting panel may include a thin film transistor and an organiclight emitting diode; and a display area 300 for the other types ofdisplay panels (e.g., plasma or electrophoretic display panels) mayinclude elements such as thin film transistors.

Referring to FIG. 1, the display area 300 includes a plurality of pixelsPX formed by the intersecting gate lines G1-Gn and data lines D1-Dm.Each pixel PX includes a thin film transistor Trsw, a liquid crystalcapacitor Clc, and a storage capacitor Cst. A control terminal of thethin film transistor Trsw is connected to a gate line. An input terminalof the thin film transistor Trsw is connected to a data line. An outputterminal of the thin film transistor Trsw is connected to a terminal ofthe liquid crystal capacitor Clc and a terminal of the storage capacitorCst. The other terminal of the liquid crystal capacitor Clc is connectedto a common electrode. A storage voltage Vcst (not shown) from thesignal controller 600 is applied to the other terminal of the storagecapacitor Cst. It should be noted that the structure of the pixel PX isnot limited to the above-described embodiment. For example, one ofordinary skill would appreciate that the structure of the pixel PX ofthe liquid crystal panel may include other embodiments and can bemodified in different ways.

As mentioned previously, the plurality of data lines D1-Dm receive thedata voltage from the data driver IC 460, and the plurality of gatelines G1-Gn receive the gate voltage from the gate driver 500.

The data driver IC 460 may be positioned on either the upper side orlower side portions of the display panel 100. In the example of FIG. 1,the data driver IC 460 is positioned on the upper side portion of thedisplay panel 100, and is connected to the data lines D1-Dm extendingvertically upwards across the display area 300.

The gate driver 500 receives clock signals CKV and CKVB, a scan startsignal STVP, and low voltages Vss1, Vss2, and Vss3. The first lowvoltage Vss1 corresponds to a gate-off voltage. The second low voltageVss2 and third low voltage Vss3 typically have lower voltage levels thanthe gate-off voltage. Based on the low voltages Vss1, Vss2, and Vss3,the gate driver 500 generates a gate voltage (which includes a gate-onvoltage and a gate-off voltage), and sequentially applies the gate-onvoltage to the gate lines G1-Gn.

Referring to FIG. 1, the clock signals CKV and CKVB, scan start signalSTVP, and low voltages Vss1, Vss2, and Vss3 are applied to the gatedriver 500 through the portion of the flexible printed circuit film 450that is positioned closest to the gate driver 500. The above signals maybe transmitted to the gate driver 500 from either an external source orthe signal controller 600, via the flexible printed circuit film 450connected to the printed circuit board (PCB) 400.

Next, the gate driver 500 and the gate lines G1-Gn will be describedwith reference to FIG. 2.

FIG. 2 shows a block diagram of the gate driver 500 and gate lines G1-Gnof FIG. 1.

Referring to FIG. 2, the display area 300 is depicted by a plurality ofresistors Rp and a plurality of capacitors Cp. The gate lines G1-Gn,liquid crystal capacitors Clc, and storage capacitors Cst haveresistances and capacitances, and the sum of the resistances andcapacitances for each gate line can be represented as a singleresistance value and a single capacitance value. As shown in FIG. 2,each gate line can be represented as a resistor Rp and a capacitor Cp ina circuit diagram. The values of the resistances Rp and capacitances Cpof the gate lines may change depending on the structure and electricalcharacteristics of the display area 300. As described below, the gatevoltage output from each stage SR in the gate driver 500 is transmittedto the respective gate line.

The gate driver 500 includes a plurality of stages SR1, SR2, SR3, SR4, .. . that are connected to one another. As shown in FIG. 2, each stageincludes four input terminals IN1, IN2, IN3, and IN4; a clock inputterminal CK; three voltage input terminals Vin1, Vin2, and Vin3; a gatevoltage output terminal OUT to output the gate voltage; a carry signaloutput terminal CRout; and an inverter signal output terminal IVTout.

The first input terminal IN1 of a stage is connected to the carry signaloutput terminal CRout of the previous stage, so as to receive the carrysignal CR of the previous stage. However, since the first stage SR1 doesnot have a previous stage, the scan start signal STVP is applied to thefirst input terminal IN1 of the first stage SR1.

The second input terminal IN2 of a stage is connected to the carrysignal output terminal CRout of the next stage, so as to receive thecarry signal CR of the next stage.

The third input terminal IN3 of a stage is connected to the carry signaloutput terminal CRout of the second next stage, so as to receive thecarry signal CR of the second next stage.

In some embodiments (not shown), the gate driver 500 may include a stageSR(n−1) connected to the (n−1)-th gate line G(n−1) and a stage SRnconnected to the n-th gate line Gn. The gate driver 500 may furtherinclude two dummy stages SR(n+1) and SR(n+2), such that the stagesSR(n−1) and SRn can receive the carry signal CR from the next stage andthe second next stage. For example, the second input terminal IN2 of thestage SRn is connected to the carry signal output terminal CRout of theSR(n+1) stage, so as to receive the carry signal CR of the SR(n+1)stage. The third input terminal IN3 of the stage SRn is connected to thecarry signal output terminal CRout of the SR(n+2) stage, so as toreceive the carry signal CR of the SR(n+2) stage.

The dummy stages SR(n+1) and SR(n+2) are stages that generate and outputa dummy gate voltage that is different from the gate voltage outputs ofthe stages SR1-SRn. As mentioned previously, the gate voltage outputsfrom the stages SR1-SRn are transmitted through the gate lines, and datavoltages are then applied to the pixels for the display of images.However, the dummy stages SR(n+1) and SR(n+2) are not connected to thegate lines, and therefore do not contribute to the display of images. Insome particular embodiments, even though the dummy stages are connectedto the gate lines, the dummy stages are connected to the gate lines ofdummy pixels (not shown) that are not used for image display.

Referring to FIG. 2, the fourth input terminal IN4 of a stage isconnected to the inverter signal output terminal IVTout of the previousstage, so as to receive the inverter signal IVT of the previous stage.However, since the first stage SR1 does not have a previous stage, asignal corresponding to an inverter signal IVT may be separatelygenerated and applied to the first stage SR1. In some embodiments, thedummy stages SR(n+1) and SR(n+2) (not shown) may generate a signal(having the same relative timing as the other stages) and transmit thesignal to the first stage SR1. In the example of FIG. 2, this signal tothe fourth input terminal IN4 of the first stage SR1 may be called as anoutput control signal OCS, which corresponds to a timing signal for oneof low voltages Vss1, Vss2, and Vss3.

A clock signal is applied to the clock terminals CK. Specifically, afirst clock signal CKV is applied to the clock terminals CK of theodd-numbered stages, and a second clock signal CKVB is applied to theclock terminals CK of the even-numbered stages. In some embodiments, thefirst clock signal CKV and the second clock signal CKVB are opposite inphase.

The low voltages Vss1, Vss2, and Vss3 are applied to the voltage inputterminals Vin1, Vin2, and Vin3, respectively. Specifically, the firstlow voltage Vss1 corresponding to the gate-off voltage is applied to thefirst voltage input terminal Vin1. The second low voltage Vss2 (that hasa lower voltage level than the first low voltage Vss1) is applied to thesecond voltage input terminal Vin2. The third low voltage Vss3 (that hasa lower voltage level than the second low voltage Vss2) is applied tothe third voltage input terminal Vin3. The values of the first lowvoltage Vss1, second low voltage Vss2 and third low voltage Vss3 may bevaried accordingly in different embodiments.

The operation of the gate driver 500 is next described.

First, the first stage SR1 receives the first clock signal CKV from anexternal source through the clock input terminal CK. The scan startsignal STVP is provided to the first input terminal IN1 of the firststage SR1. The first to third low voltages Vss1, Vss2, and Vss3 areprovided to the first to third voltage input terminals Vin1, Vin2, andVin3 of the first stage SR1, respectively. The carry signals CR from thecarry signal output terminal CRout of the second stage SR2 are providedto the second input terminal IN2 of the first stage SR1. The carrysignals CR from the carry signal output terminal CRout of the thirdstage SR3 are provided to the third input terminal IN3 of the firststage SR1. The output control signal OCS is provided to the fourth inputterminal IN4 of the first stage SR1, such that the gate-on voltage isoutput to the first gate line G1 through the gate voltage outputterminal OUT of the first stage SR1. The carry signal output terminalCRout of the first stage SR1 outputs the carry signal CR to the firstinput terminal IN1 of the second stage SR2. The inverter signal outputterminal IVTout of the first stage SR1 transmits the inverter signal IVTto the fourth input terminal IN4 of the second stage SR2.

The second stage SR2 receives the second clock signal CKVB from theexternal source through the clock input terminal CK. The first inputterminal IN1 of the second stage SR2 receives the carry signal CR fromthe carry signal output terminal CRout of the first stage SR1. The firstto third low voltages Vss1, Vss2, and Vss3 are provided to the first tothird voltage input terminals Vin1, Vin2, and Vin3 of the second stageSR2, respectively. The carry signals CR from the carry signal outputterminal CRout of the third stage SR3 are provided to the second inputterminal IN2 of the second stage SR2. The carry signals CR from thecarry signal output terminal CRout of the fourth stage SR4 are providedto the third input terminal IN3 of the second stage SR2. The fourthinput terminal IN4 of the second stage SR2 receives the inverter signalIVT from the inverter signal output terminal IVTout of the first stageSR1, such that the gate-on voltage is output to the second gate line G2through the gate voltage output terminal OUT of the second stage SR2.The carry signal CR from the carry signal output terminal CRout of thesecond stage SR2 is provided to the first input terminal IN1 of thethird stage SR3 and the second input terminal IN2 of the first stageSR1. The inverter signal output terminal IVTout of the second stage SR2transmits the inverter signal IVT to the fourth input terminal IN4 ofthe third stage SR3.

The third stage SR3 receives the first clock signal CKV from theexternal source through the clock input terminal CK. The first inputterminal IN1 of the third stage SR3 receives the carry signal CR fromthe carry signal output terminal CRout of the second stage SR2. Thefirst to third low voltages Vss1, Vss2, and Vss3 are provided to thefirst to third voltage input terminals Vin1, Vin2, and Vin3 of the thirdstage SR3, respectively. The carry signals CR from the carry signaloutput terminal CRout of the fourth stage SR4 are provided to the secondinput terminal IN2 of the third stage SR3. The carry signals CR from thecarry signal output terminal CRout of the fifth stage SR5 (not shown)are provided to the third input terminal IN3 of the third stage SR3. Thefourth input terminal IN4 of the third stage SR3 receives the invertersignal IVT from the inverter signal output terminal IVTout of the secondstage SR2, such that the gate-on voltage is output to the third gateline G3 through the gate voltage output terminal OUT of the third stageSR3. The carry signal CR from the carry signal output terminal CRout ofthe third stage SR3 is provided to the first input terminal IN1 of thefourth stage SR4, the second input terminal IN2 of the second stage SR2,and the third input terminal IN3 of the first stage SR1. The invertersignal output terminal IVTout of the third stage SR3 transmits theinverter signal IVT to the fourth input terminal IN4 of the fourth stageSR4.

Consistent with the above, the n-th stage SRn receives the second clocksignal CKVB from the external source through the clock input terminalCK. The first input terminal IN1 of the n-th stage SRn receives thecarry signal CR from the carry signal output terminal CRout of the(n−1)-th stage SR(n−1). The first to third low voltages Vss1, Vss2, andVss3 are provided to the first to third voltage input terminals Vin1,Vin2, and Vin3 of the n-th stage SRn, respectively. The carry signals CRfrom the carry signal output terminal CRout of the (n+1)-th stageSR(n+1) (dummy stage) are provided to the input terminal IN2 of the n-thstage SRn. The carry signals CR from the carry signal output terminalCRout of the (n+2)-th stage SR(n+2) (dummy stage) are provided to thethird input terminal IN3 of the n-th stage SRn. The fourth inputterminal IN4 of the n-th stage SRn receives the inverter signal IVT fromthe inverter signal output terminal IVTout of the (n−1)-th stageSR(n−1), such that the gate-on voltage is output to the n-th gate lineGn through the gate voltage output terminal OUT of the n-th stage SRn.The carry signal CR from the carry signal output terminal CRout of then-th stage SRn is provided to the first input terminal IN1 of the(n+1)-th stage SR(n+1) (dummy stage), the second input terminal IN2 ofthe (n−1)-th stage SR(n−1), and the third input terminal IN3 of the(n−2)-th stage (SRn−2). The inverter signal output terminal IVTout ofthe n-th stage SRn transmits the inverter signal IVT to the fourth inputterminal IN4 of the (n+1)-th stage SR(n+1) (dummy stage).

The connections between the stages SR of the gate driver 500 has beendescribed above with reference to FIG. 2. Next, the circuit layout of astage SR will be described in further detail with reference to FIG. 3.

FIG. 3 is a circuit diagram of a stage in a gate driver according to anexemplary embodiment of the inventive concept.

Referring to FIG. 3, a stage SR of the gate driver 500 includes anoutput unit 511, an inverter unit 512, a carry signal generator 513, a Qnode stabilization unit 514, an I node stabilization unit 515, and apull-down unit 516.

The output unit 511 includes a transistor (e.g., first transistor T1)and a capacitor (e.g., first capacitor C1). The control terminal of thefirst transistor T1 is connected to a node Q (hereinafter referred to asthe first node). The input terminal of the first transistor T1 receivesthe first clock signal CKV or the second clock signal CKVB through theclock terminal CK. The first capacitor C1 is formed between the controlterminal and the output terminal of the first transistor T1. The outputterminal of the first transistor T1 is connected to the gate voltageoutput terminal OUT. The output terminal of the first transistor T1 isalso connected to the pull-down unit 516. Specifically, the outputterminal of the first transistor T1 is connected to the first voltageinput terminal Vin1 through the pull-down unit 516. As a result, thevalue of the gate-off voltage corresponds to the first low voltage Vss1.The output unit 511 outputs the gate voltage according to the voltage ofthe node Q and the first clock signal CKV. A voltage difference isgenerated between the control terminal and the output terminal of thefirst transistor T1 by the voltage of the node Q. If charge from thevoltage difference is stored in the first capacitor C1 and a highvoltage is subsequently applied through the clock signal, the highvoltage will be output as the gate-on voltage so long as the firstcapacitor C1 is charged.

Referring to FIG. 3, the inverter unit 512 includes four transistors(twelfth transistor T12, seventh transistor T7, eighth transistor T8,and thirteenth transistor T13). The input terminal and the controlterminal of the twelfth transistor T12 are connected together by a diodeconnection that is connected to the clock input terminal CK. The outputterminal of the twelfth transistor T12 is connected to the controlterminal of the seventh transistor T7 and the input terminal of thethirteenth transistor T13. The input terminal of the seventh transistorT7 is connected to the clock input terminal CK, and the output terminalof the seventh transistor T7 is connected to a node I (referred to asthe inverter node or the second node). As mentioned above, the controlterminal of the seventh transistor T7 is connected to the outputterminal of the twelfth transistor T12. The control terminal of theeighth transistor T8 is connected to the transmitting signal outputterminal CRout of the current stage. The input terminal of the eighthtransistor T8 is connected to the node I, and the output terminal of theeighth transistor T8 is connected to the second voltage input terminalVin2. As mentioned above, the input terminal of the thirteenthtransistor T13 is connected to the output terminal of the twelfthtransistor T12. The control terminal of the thirteenth transistor T13 isconnected to the transmitting signal output terminal CRout of thecurrent stage. The output terminal of the thirteenth transistor T13 isconnected to the second voltage input terminal Vin2. A clock signal istransmitted to the input terminals of the eighth and thirteenthtransistors T8 and T13 by the twelfth and seventh transistors T12 andT7. If the clock signal is applied with a high voltage, the node I willbe at high voltage. However, the transmitted high voltage signal willreduce the voltage of the node I to the second low voltage VSS2 when thetransmitting signal output terminal CRout of the current stage outputsthe transmitting signal CR. As a result, the node I of the inverter unit512 has a reverse voltage level with respect to the transmitting signalCR of the current stage and the gate-on voltage.

Referring to FIG. 3, the carry signal generator 513 includes atransistor (fifteenth transistor T15). The input terminal of thefifteenth transistor T15 is connected to the clock terminal CK, so as toreceive the first clock signal CKV or second clock signal CKVB. Thecontrol terminal of the fifteenth transistor T15 is connected to thecontrol terminal of the input section 511 (first transistor T1) via nodeQ. The output terminal of the fifteenth transistor T15 is connected tothe carry signal output terminal CRout that outputs the carry signal CR.In some embodiments, a parasitic capacitance (not shown) may be formedbetween the control terminal and the output terminal of the fifteenthtransistor T15. The output terminal of the fifteenth transistor T15 isalso connected to the eleventh transistor T11 and the seventeenthtransistor T17 of the pull-down unit 516, thereby receiving the thirdlow voltage Vss3. As a result, when the carry signal CR is low, thevoltage of the carry signal CR corresponds to the third low voltageVss3.

Referring to FIG. 3, the Q node stabilization unit 514 includes fourtransistors (fourth transistor T4, sixth transistor T6, ninth transistorT9, and tenth transistor T10). The input terminal and the controlterminal of the fourth transistor T4 are commonly connected(diode-connected) to the first input terminal IN1, and the outputterminal of the fourth transistor T4 is connected to the node Q. Thefourth transistor T4 transmits the high voltage to the node Q when thefirst input terminal IN1 is applied with the high voltage. The controlterminal of the sixth transistor T6 is connected to the third inputterminal IN3. The input terminal of the sixth transistor T6 is connectedto the node Q, and the output terminal of the sixth transistor T6 isconnected to the second voltage input terminal Vin2. The sixthtransistor T6 changes the voltage of the node Q to the second lowvoltage Vss2 when the carry signal CR of the second next stage isapplied with the high voltage. The control terminal of the ninthtransistor T9 is connected to the second input terminal IN2. The inputterminal of the ninth transistor T9 is connected to the node Q, and theoutput terminal of the ninth transistor T9 is connected to the secondvoltage input terminal Vin2. As a result, when the carry signal CR ofthe next stage is applied with the high voltage, the voltage of the nodeQ corresponds to the second low voltage Vss2. The control terminal ofthe tenth transistor T10 is connected to the node I. The input terminalof the tenth transistor T10 is connected to the node Q and the outputterminal of the tenth transistor T10 is connected to the second voltageinput terminal Vin2. The tenth transistor T10 changes the voltage of thenode Q to the second low voltage Vss2 via the high voltage output of theinverter unit 512. The voltage of the node Q is stabilized in each timeperiod by the fourth transistor T4, sixth transistor T6, ninthtransistor T9, and tenth transistor T10 connected to the node Q.

Referring to FIG. 3, the I node stabilization unit 515 includes atransistor (fifth transistor T5). The input terminal of the fifthtransistor T5 is connected to the node I. The control terminal of thefifth transistor T5 is connected to the first input terminal IN1, andthe output terminal of the fifth transistor T5 is connected to thesecond voltage input terminal Vin2. The fifth transistor T5 reduces thevoltage of the node I to the second low voltage Vss2 when the highvoltage is applied to the first input terminal IN1.

The pull-down unit 516 includes five transistors (second transistor T2,third transistor T3, eleventh transistor T11, eleventh-1 transistorT11-1, and seventeenth transistor T17) connected to the output unit 511and output terminal of the carry signal generator 513. The controlterminal of the second transistor T2 is connected to the second inputterminal IN2. The input terminal of the second transistor T2 isconnected to the gate voltage output terminal OUT, and the outputterminal of the second transistor T2 is connected to the first voltageinput terminal Vin1. The second transistor T2 changes the voltage of thegate voltage output terminal OUT to the first low voltage Vss1 accordingto the transmitting signal CR of the next stage. The control terminal ofthe third transistor T3 is connected to the node I. The input terminalof the third transistor T3 is connected to the gate voltage outputterminal OUT, and the output terminal of the third transistor T3 isconnected to the first voltage input terminal Vin1. The third transistorT3 changes the voltage of the gate voltage output terminal OUT to thefirst low voltage Vss1 according to the voltage of the node I. Thecontrol terminal of the eleventh transistor T11 is connected to the nodeI. The input terminal of the eleventh transistor T11 is connected to thecarry signal output terminal CRout, and the output terminal of theeleventh transistor T11 is connected to the third voltage input terminalVin3. The eleventh transistor T11 changes the voltage of the carrysignal output terminal CRout to the third low voltage Vss3 according tothe voltage of the node I. The control terminal of the eleventh-1transistor T11-1 is connected to the fourth input terminal IN4. Theinput terminal of the eleventh-1 transistor T11-1 is connected to thegate voltage output terminal OUT, and the output terminal of theeleventh-1 transistor T11-1 is connected to the first voltage inputterminal Vin1. The eleventh-1 transistor T11-1 changes the gate voltageto the first low voltage Vss1 when the inverter output signal of theprevious stage is applied with the high voltage. The control terminal ofthe seventeenth transistor T17 is connected to the second input terminalIN2. The input terminal of the seventeenth transistor T17 is connectedto the carry signal output terminal CRout, and the output terminal ofthe seventeenth transistor T17 is connected to the third voltage inputterminal Vin3. The seventeenth transistor T17 changes the voltage of thecarry signal output terminal CRout to the third low voltage Vss3according to the carry signal of the next stage.

The low voltages Vss1, Vss2, and Vss3, clock signal voltage, gatevoltage value, and value of the carry signal may have differentvoltages. For example, in some embodiments, the first low voltage Vss1is −7 V, the second low voltage Vss2 is −11 V, the third low voltageVss3 is −15 V, and the voltage of the clock signal is between 15 V and−15 V. The gate-on voltage can have different voltage values dependingon the characteristics of the output unit 511. The gate-off voltagecorresponds to the first low voltage Vss1. The high voltage of the carrysignal can have different values depending on the characteristic of thecarry signal generator 513. The low voltage corresponds to the third lowvoltage Vss3.

Next, the operation of the stage in FIG. 3 will be described.

The carry signal generator 513 and the output unit 514 are operatedbased on the voltage of the node Q such that a stage SR outputs the highvoltage of the carry signal CR and the gate-on voltage. The carry signalCR is reduced from the high voltage to the third low voltage Vss3 basedon the output of the inverter unit 512 of the current stage and thecarry signal CR of the next stage. The gate-on voltage is reduced fromthe high voltage to the first low voltage Vss1 (or gate-off voltage)based on the output of the inverter unit 512 of the current stage andthe carry signals CR of the next stage and the second next stage.

The Q node stabilization unit 514 and the I node stabilization unit 515stabilize the voltages at the node Q and the node I, respectively, asthe gate voltage and the carry signal CR are periodically changed.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −4 V, the Vgs of the ninthtransistor T9 is −4 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is −4 V.

As shown above, the Vgs of the fourth transistor T4, the sixthtransistor T6, the ninth transistor T9 and the tenth transistor T10 havea value of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein leakage current, the voltage of the node Q may be maintained at aconstant level. As a result, the voltage of the node Q is stabilized.

The transistors in each stage may be formed in the same process as thethin film transistor Trsw of FIG. 1. In other words, the transistors ineach stage may be formed together with the plurality of pixels in thedisplay area 300. The semiconductor material that is used to form thechannel of the thin film transistor Trsw and the transistors of eachstage may include amorphous silicon or an oxide semiconductor such asIGZO. However, the two semiconductor materials (amorphous silicon andoxide semiconductor) have different electrical characteristics andprocess requirements. As a result, if IGZO oxide semiconductor isincluded in the transistors of FIG. 3, amorphous silicon may not beused.

The difference in the electrical characteristics of the amorphoussilicon and the oxide semiconductor will be described with reference toFIG. 4. FIG. 4 depicts I-V (current-voltage) curves for a transistorincluding an amorphous silicon semiconductor and a transistor includingan oxide semiconductor.

In FIG. 4, the left graph (ASG) depicts the I-V curve for an amorphoussilicon gate and the right graph (OSG) depicts the I-V curve for anoxide semiconductor gate. As mentioned previously, the oxidesemiconductor can include IGZO. In both graphs, the horizontal axisrepresents the Vgs voltage and the vertical axis represents the value ofa current flowing to the channel.

With reference to the left graph (ASG), in the amorphous silicontransistor, the current generally decreases with the voltage Vgs untilthe voltage Vgs is about −10 V, and increases slightly when the voltageVgs is further reduced below −10 V. This slight increase in currentgives rise to leakage current which causes the transistor performance todeteriorate. Thus, in the amorphous silicon transistor, the voltage Vgsmay not be less than a predetermined value (e.g., −10 V). Accordingly,when the voltage applied to the stage is lower than the predeterminedvalue (e.g., −10 V), the driving characteristic of the stagedeteriorates.

Referring to the right graph (OSG), in the oxide semiconductortransistor, the current generally decreases with the voltage Vgs untilthe voltage Vgs is about −5 V, and remains relatively constant when thevoltage Vgs is further reduced below −5 V. As a result, the oxidesemiconductor transistor is less prone to leakage current than theamorphous silicon transistor at low voltage levels.

Thus, in applications where the voltage Vgs is less than −10 V, theoxide semiconductor (such as IGZO) transistor is preferred over theamorphous silicon transistor.

In the example of FIG. 3, the third low voltage Vss3 and the voltage ofthe clock signal are assigned a same value of −15 V. By assigning commonvoltage values to different signals, the number of different voltagesgenerated in the display panel can be reduced, which simplifies therequirements for the driving voltage generator. Since the third lowvoltage Vss3 and the voltage of the clock signal are less than −10 V, anoxide semiconductor (instead of amorphous silicon) is used as thechannel material in the transistors of FIG. 3.

In some embodiments, a region occupied by the gate driver can be reducedsince the channel sizes of transistors are smaller when the oxidesemiconductor is used as the material in the channel layer, as describedbelow with reference to FIG. 5.

FIG. 5 is a view of the area occupied by a gate driver according to anexemplary embodiment of the inventive concept.

As shown in FIG. 5, a light blocking member BM positioned outside thedisplay area 300 is formed with a width of about 2 mm. The gate driverOSG (incorporating the oxide semiconductor) may be formed with a widthof about 0.65 mm. In some embodiments, the width of the light blockingmember BM may be further reduced so as to realize a slim bezel.

FIG. 6 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment of the inventive concept. The circuit ofFIG. 6 is similar to the circuit of FIG. 3, except the levels of theapplied voltages VSS1 and VSS2 in FIG. 6 are different from those inFIG. 3.

In the example of FIG. 6, the first low voltage Vss1 is −9 V and thesecond low voltage Vss2 is −12 V, which are different from the first lowvoltage Vss1 of −7 V and second low voltage Vss2 of −11 V in FIG. 3. Inboth FIGS. 3 and 6, the third low voltage Vss3 is −15 V and the voltageof the clock signal is between 15 V and −15 V.

The change in voltage changes the low voltage of the gate-off voltageand the carry signal CR. however the voltage is only decreased in thedisplay panel and images displayed on the display panel are not changedduring the driving since those voltages are not applied to the inside ofpixels. However, in the output of the Q node stabilization unit 514 andthe inverter unit 512, the voltage change is generated as follows.

The voltage Vgs is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −3 V, the Vgs of the ninthtransistor T9 is −3 V, and the Vgs of the tenth transistor T10 is 0 V.Also, in the inverter unit 512, the Vgs of the eighth transistor T8connected to the output terminal is −3 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 6, since the lowest applied voltage is −15 V, theoxide semiconductor (such as IGZO) is used as the channel material inthe transistors of FIG. 6.

Next, the high temperature reliability of the embodiments in FIGS. 3 and6 will be described with reference to FIGS. 7 and 8.

FIGS. 7 and 8 are tables showing the output characteristics of exemplarygate drivers under different operating conditions. Specifically, FIG. 7shows the change in the gate voltage and the voltage of the node Q withtime for the embodiments of FIGS. 3 and 6 as well as a comparativeexample.

The comparative example is a circuit which does not have a third lowvoltage Vss3 element. Also, in the comparative example, the second lowvoltage Vss2 is connected to transistors instead of the third lowvoltage Vss3.

In FIG. 7 (a), the channel length of the transistor is 7 μm. In FIG. 7(b), the channel length of the transistor is 3 μm.

Referring to FIGS. 7 (a) and 7 (b), it is observed that the embodimentsof FIGS. 3 and 6 and the comparative example have similar gate voltages.However, the comparative example undergoes a decrease in the voltage ofthe node Q (relative to the embodiments of FIGS. 3 and 6) at certaintime intervals. For example, the magnitude of the decrease in voltage ofthe node Q (ΔVqnode) between the comparative example and the embodimentsin FIGS. 3 and 6 is about 11.8 V in FIG. 7 (a) and about 17.6 V in FIG.7 (b).

The voltage drop of the node Q in the comparative example may impact thegeneration of the gate voltage. Although the gate voltage in thecomparative example can be generated without issues at room temperature,reliability issues may arise when the gate voltage in the comparativeexample is generated at a high temperature or a low temperature, asdescribed below with reference to FIG. 8.

FIG. 8 shows the high temperature characteristics of the embodiments ofFIGS. 3 and 6 and the comparative example.

As shown in FIG. 8, the embodiments of FIGS. 3 and 6 and the comparativeexample have a typical characteristic of 90% which is more than thereference standard of 80%. In other words, the embodiments of FIGS. 3and 6 and the comparative example should not experience reliabilityproblems when operated at room temperature.

However, when the threshold voltage Vth is −2 V (negative Vth) andoperation is carried out at high temperature, the characteristic of thecomparative example drops to about 65% to 70%, which is lower than thereference standard of 80%. Under these operating conditions (negativeVth and high temperature), defects may be generated in the devices inthe comparative example, which may then lead to reliability issues.Nonetheless, as shown in the rightmost column in the table of FIG. 8,the long term reliability of the comparative example is still higherthan that of the reference standard. Accordingly, the comparativeexample can still be used so long as it is not subject to hightemperature for long periods of time.

Conversely, the operation characteristics of the comparative example maydeteriorate under low temperature conditions. To mitigate the lowtemperature characteristics, an additional circuit can be separatelyformed (or added) to the comparative example. Accordingly, thecharacteristics at low temperatures can be improved using a compensationcircuit, thereby maintaining the long term reliability of the gatedriver.

Next, different embodiments of the inventive concept will be describedwith reference to FIGS. 9 to 17.

FIGS. 9 to 17 are circuit diagrams of a stage in a gate driver accordingto different embodiments of the inventive concept.

FIG. 9 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. Other than the voltage values of the lowvoltage and the clock signal, the circuit of FIG. 9 is the same as thecircuits of FIGS. 3 and 6.

In the example of FIG. 9, the first low voltage Vss1 is −6 V, the secondlow voltage Vss2 is −8 V, and the third low voltage Vss3 is −10 V. Thevoltage of the clock signal is between 20 V and −10 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −2 V, the Vgs of the ninthtransistor T9 is −2 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is −2 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 9, since the lowest applied voltage is −10 V,either amorphous silicon or oxide semiconductor may be used as thechannel material in the transistors of FIG. 9.

FIG. 10 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. Other than the levels of the appliedvoltages, the circuit of FIG. 10 is the same as the circuits of FIGS. 3,6, and 9.

In the example of FIG. 10, the first low voltage Vss1 is −7 V, thesecond low voltage Vss2 is −11 V, and the third low voltage Vss3 is −15V, which are the same as the low voltages in FIG. 3. Unlike FIG. 3, thevoltage of the clock signal in FIG. 10 is between 15 V and −11 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is 0 V, the Vgs of the ninthtransistor T9 is 0 V, and Vgs of the tenth transistor T10 is 0 V. Also,the Vgs of the eighth transistor T8 connected to the output terminal inthe inverter unit 512 is −4 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 10, since the lowest applied voltage correspondsto the third low voltage Vss3 of −15 V, the oxide semiconductor is usedas the channel material in the transistors of FIG. 10.

FIG. 11 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. The circuit of FIG. 11 is different fromthe circuit of FIG. 3, as described below.

In the example of FIG. 11, the output terminal of the eleventhtransistor T11 of the pull-down unit 516 is connected to the secondvoltage input terminal Vin2. Accordingly, the eleventh transistor T11changes the voltage of the carry signal output terminal CRout to thesecond low voltage Vss2 according to the voltage of the node I. Thecarry signal CR is not applied to an actual pixel. As a result, imagedisplay of the pixel is not affected by the change in the level of thelow voltage.

In the example of FIG. 11, the first low voltage Vss1 is −7 V, thesecond low voltage Vss2 is −11 V, and the third low voltage Vss3 is −15V, which are the same as the low voltages in FIG. 3. Like FIG. 3, thevoltage of the clock signal in FIG. 11 is between 15 V and −15 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −4 V, the Vgs of the ninthtransistor T9 is −4 V, and the Vgs of the tenth transistor T10 is −4 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is 0 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 11, since the lowest applied voltage is −15 V,the oxide semiconductor is used as the channel material in thetransistors of FIG. 11.

FIG. 12 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. The circuit of FIG. 12 is different fromthe circuit of FIG. 3, as described below.

In the example of FIG. 12, the output terminals of the sixth transistorT6 and the ninth transistor T9 of the Q node stabilization unit 514 areconnected to the third low voltage Vss3. The control terminal of thesixth transistor T6 is connected to the third input terminal IN3. Theinput terminal of the sixth transistor T6 is connected to the node Q,and the output terminal of the sixth transistor T6 is connected to thethird voltage input terminal Vin3. When the carry signal CR of thesecond next stage is applied with the high voltage, the sixth transistorT6 changes the voltage of the node Q to the third low voltage Vss3. Thecontrol terminal of the ninth transistor T9 is connected to the secondinput terminal IN2. The input terminal of the ninth transistor T9 isconnected to the node Q, and the output terminal of the ninth transistorT9 is connected to the third voltage input terminal Vin3. As a result,when the carry signal CR of the next stage is applied with the highvoltage, the voltage of the node Q changes to the third low voltageVss3. The sixth transistor T6 and the ninth transistor T9 change thenode Q to the third low voltage Vss3 (that has a lower voltage levelthan the second low voltage Vss2). This reduces the leakage currentgenerated in the transistor connected to the node Q and as a result, thevoltage of the node Q can be maintained at a constant. Accordingly, thevoltage of the node Q is stabilized.

In the example of FIG. 12, the first low voltage Vss1 is −7 V, thesecond low voltage Vss2 is −11 V, and the third low voltage Vss3 is −15V, which are the same as the low voltages in FIG. 3. Like FIG. 3, thevoltage of the clock signal in FIG. 12 is between 15 V and −15 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is 0 V, the Vgs of the ninthtransistor T9 is 0 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is −4 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 12, since the lowest applied voltage is −15 V,the oxide semiconductor is used as the channel material in thetransistors of FIG. 12.

FIG. 13 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. The circuit in FIG. 13 is different fromthe circuit in FIG. 3, as described below.

In the example of FIG. 13, the control terminal of the ninth transistorT9 of the Q node stabilization unit 514 is connected to the second lowvoltage Vss2. The output terminal of the ninth transistor T9 isconnected to the third low voltage Vss3. The output terminal of theeighth transistor T8 of the inverter unit 512 is also connected to thethird low voltage Vss3.

The control terminal of the ninth transistor T9 is connected to thesecond voltage input terminal Vin2. The input terminal of the ninthtransistor T9 is connected to the node Q and the output terminal of theninth transistor T9 is connected to the third voltage input terminalVin3. By applying the second low voltage Vss2 to the control terminal ofthe ninth transistor T9, the turn-off state may be continuouslymaintained, so as to prevent voltage leakage at the node Q. As mentionedabove, the output terminal of the eighth transistor T8 is connected tothe third low voltage Vss3. The output of the inverter unit 512 isprovided at node I which has the third low voltage Vss3 as the lowvoltage. Thus, when the gate-on voltage is output, the voltage of thenode I and the output of the inverter unit 512 are at the third lowvoltage Vss3. Accordingly, the leakage current can be controlled.

In the example of FIG. 13, the first low voltage Vss1 is −7 V, thesecond low voltage Vss2 is −11 V, and the third low voltage Vss3 is −15V, which are the same as the low voltages in FIG. 3. Like FIG. 3, thevoltage of the clock signal is between 15 V and −15 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −4 V, the Vgs of the ninthtransistor T9 is −4 V, and the Vs of the tenth transistor T10 is −4 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is 0 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 13, since the lowest applied voltage is −15V, theoxide semiconductor is used as the channel material in the transistorsof FIG. 13.

Next, the embodiments of FIGS. 14 and 15 will be described. In theexamples of FIGS. 14 and 15, the third voltage input terminal Vin3applying the third low voltage Vss3 and the wiring connected thereto isremoved. As a result, the third low voltage Vss3 is omitted. Theeleventh-1 transistor 11-1 is also omitted in the examples of FIGS. 14and 15.

As described previously in FIG. 3, the output terminals of the eleventhtransistor T11 and the seventeenth transistor T17 of the pull-down unit516 are connected to the third low voltage Vss3. However, in the exampleof FIG. 14, the output terminal of the eleventh transistor T11 of thepull-down unit 516 is connected to the second low voltage Vss2. Theoutput terminal of the seventeenth transistor T17 of the pull-down unit516 is not connected to the second low voltage Vss2 in FIG. 14.Accordingly, the low voltage of the carry signal CR is the second lowvoltage Vss2 in FIG. 14.

Referring back to FIGS. 7 and 8, the comparative example (in which thethird low voltage Vss3 is not applied) was described. Since the lowvoltage Vss3 is not applied in FIG. 14, the example of FIG. 14 mayinclude operation characteristics similar to those of the comparativeexample described in FIGS. 7 and 8. For example, operating theembodiment of FIG. 14 at high temperature may cause the operationcharacteristics to deteriorate. Thus, in order to maintain long termreliability, the exemplary embodiment of FIG. 14 is preferably operatedat room temperature conditions.

It is noted that the example of FIG. 14 can include different first andsecond low voltages. Also, the voltage of the clock signal in theexample of FIG. 14 may be the same as (or different from) the voltagesof the clock signal described in the other embodiments.

In the example of FIG. 14, the first low voltage Vss1 is −5 V, thesecond low voltage Vss2 is −10 V, and the voltage of the clock signal isbetween 15 V and −15 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −5 V, the Vgs of the ninthtransistor T9 is −5 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is 0 V.

As shown above, the Vgs voltage of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 14, since the lowest applied voltage is −15 V,the oxide semiconductor is used as the channel material in thetransistors of FIG. 14.

FIG. 15 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment. The circuit of FIG. 15 is different fromthe circuit of FIG. 14, in that the output terminal of the eleventhtransistor T11 in FIG. 15 is connected to the first low voltage Vss1.

In the example of FIG. 15, the first low voltage Vss1 is −5 V, thesecond low voltage Vss2 is −10 V, and the voltage of the clock signal isbetween 15 V and −15 V, which are the same as the example of FIG. 14.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −5 V, the Vgs of the ninthtransistor T9 is −4 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is −5 V.

In the example of FIG. 15, the voltage leakage at the node I (the outputof the inverter unit 512) is decreased when the Vgs of the eighthtransistor T8 is reduced.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 15, since the lowest applied voltage is −15 V,the oxide semiconductor is used as the channel material in thetransistors of FIG. 15.

FIG. 16 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment.

The output unit 511, the inverter unit 512, the carry signal generator513, and the Q node stabilization unit 514 in FIG. 16 are the same asthose described in FIG. 3. Unlike FIG. 3, the fifth transistor T5forming the I node stabilization unit 515 and the eleventh-1 transistorT11-1 and the seventeenth transistor T17 forming the pull-down unit 516are omitted in the example of FIG. 16.

Referring to FIG. 16, the pull-down unit 516 includes three transistors(the second transistor T2, the third transistor T3, and the eleventhtransistor T11) connected to the output unit 511 and the output terminalof the carry signal generator 513. The control terminal of the secondtransistor T2 is connected to the second input terminal IN2. The inputterminal of the second transistor T2 is connected to the gate voltageoutput terminal OUT, and the output terminal of the second transistor T2is connected to the first voltage input terminal Vin1. The secondtransistor T2 changes the voltage of the gate voltage output terminalOUT to the first low voltage Vss1 according to the next stage carrysignal CR. The control terminal of the third transistor T3 is connectedto the node I. The input terminal of the third transistor T3 isconnected to the gate voltage output terminal OUT, and the outputterminal of the third transistor T3 is connected to the first voltageinput terminal Vin1. The third transistor T3 changes the voltage of thegate voltage output terminal OUT to the first low voltage Vss1 accordingto the voltage of the node I. The control terminal of the eleventhtransistor T11 is connected to the node I. The input terminal of theeleventh transistor T11 is connected to the carry signal output terminalCRout, and the output terminal of the eleventh transistor T11 isconnected to the third voltage input terminal Vin3. The eleventhtransistor T11 changes the voltage of the carry signal output terminalCRout to the third low voltage Vss3 according to the voltage of the nodeI.

In the example of FIG. 16, the first low voltage Vss1 is −5 V, thesecond low voltage Vss2 is −10 V, and the third low voltage Vss3 is −15V. The voltage of the clock signal is between 15 V and −15 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the sixth transistor T6 is −5 V, the Vgs of the ninthtransistor T9 is −5 V, and the Vgs of the tenth transistor T10 is 0 V.Also, the Vgs of the eighth transistor T8 connected to the outputterminal in the inverter unit 512 is −5 V.

As shown above, the Vgs voltages of the fourth transistor T4, the sixthtransistor T6, ninth transistor T9 and the tenth transistor T10 have avalue of equal to or less than 0 V, so as to generate and output thegate-on voltage in the corresponding stage. Since there is no increasein the leakage current, the voltage of the node Q may be maintained at aconstant. As a result, the voltage of the node Q is stabilized.

In the example of FIG. 16, since the lowest applied voltage is −15 V,the oxide semiconductor is used as the channel material in thetransistors of FIG. 16.

As mentioned previously, the voltage level in the example of FIG. 16 canbe modified. If the lowest applied voltage in the example of FIG. 16 ischanged to −10 V, amorphous silicon (instead of the oxide semiconductor)may be used as the channel material in the transistors of FIG. 16.

FIG. 17 is a circuit diagram of a stage in a gate driver according toanother exemplary embodiment.

The output unit 511, the inverter unit 512, and the carry signalgenerator 513 in FIG. 17 are the same as those described in FIG. 3.Unlike FIG. 3, the fifth transistor T5 forming the I node stabilizationunit 515 is omitted and the connections of the seventeenth transistor T7of the pull-down unit 516 are modified in the example of FIG. 17. Thestructure of the Q node stabilization unit 514 in FIG. 17 is alsodifferent from that of FIG. 3.

Since the output unit 511, inverter unit 512, and carry signal generator513 in FIG. 17 are the same as those described previously in FIG. 3,detailed description of the aforementioned elements shall be omitted.

Referring to FIG. 17, the Q node stabilization unit 514 includes fivetransistors (the fourth transistor T4, the ninth transistor T9, theninth-1 transistor T9-1, the tenth transistor T10, and the tenth-1transistor T10-1). The input terminal and the control terminal of thefourth transistor T4 are commonly connected to the first input terminalIN1 (by a diode connection), and the output terminal of the fourthtransistor T4 is connected to the node Q. When the high voltage isapplied to the first input terminal IN1, the fourth transistor T4applies the high voltage to the node Q.

The ninth and ninth-1 transistors T9 and T9-1 form a pair of transistorsin which an input terminal and an output terminal of the transistors areconnected to each other and the control terminals are connected to asame terminal. As shown in FIG. 17, the output terminal of the ninthtransistor T9 is connected to the input terminal of the ninth-1transistor T9-1. The control terminals of the ninth and ninth-1transistors T9 and T9-1 are connected to the second input terminal IN2.The input terminal of the ninth transistor T9 is connected to the nodeQ. The output terminal of the ninth-1 transistor T9-1 is connected tothe second voltage input terminal Vin2. By using a pair of connectiontransistors, the two transistors divide the voltage (particularly thelow voltage) difference between the second low voltage and the carrysignal of the next stage to be applied, such that leakage current at thenode Q is minimized. In some embodiments, the ninth and ninth-1transistors T9 and T9-1 may be formed having a structure in which atleast three additional thin film transistors are connected. In thoseembodiments, the input terminals and the output terminals of theadditional transistors may be connected to each other, and the controlterminals of the additional transistors may be connected to the samesecond input terminal IN2.

In some embodiments, the tenth and tenth-1 transistors T10 and T10-1form a pair of transistors in which an input terminal and an outputterminal of the transistors are connected to each other and the controlterminals are connected to a same terminal. As shown in FIG. 17, theoutput terminal of the tenth transistor T10 is connected to the inputterminal of the tenth-1 transistor T10-1. The control terminals of thetenth and tenth-1 transistors T10 and T10-1 are connected to the node I.The input terminal of the tenth transistor T10 is connected to the nodeQ and the output terminal of the tenth-1 transistor T10-1 is connectedto the second voltage input terminal Vin2. The tenth and the tenth-1transistors T10 and T10-1 change the voltage of the node Q to the secondlow voltage Vss2 according to the voltage of the node I. By using a pairof connection transistors, the two transistors divide the voltagedifference between the second low voltage and the node I to be applied,such that leakage current at the node Q is minimized. In someembodiments, the tenth and tenth-1 transistors T9 and T9-1 may be formedhaving a structure in which at least additional three thin filmtransistors are connected. In those embodiments, the input terminals andthe output terminals of the additional transistors may be connected toeach other, and the control terminals of the additional transistors maybe connected to the same node I.

When the fourth transistor T4, ninth transistor T9, ninth-1 transistorT9-1, tenth transistor T10, and tenth-1 transistor T10-1 are connectedto the node Q, the voltage of the node Q is stabilized in each timeperiod.

The pull-down unit 516 in FIG. 17 is described as follows.

The pull-down unit 516 includes five transistors (the second transistorT2, the third transistor T3, the eleventh transistor T11, the eleventh-1transistor T11-1, and the seventeenth transistor T17) connected to theoutput unit 511 and the output terminal of the carry signal generator513.

The control terminal of the second transistor T2 is connected to thesecond input terminal IN2. The input terminal of the second transistorT2 is connected to the gate voltage output terminal OUT, and the outputterminal of the second transistor T2 is connected to the first voltageinput terminal Vin1. The second transistor T2 changes the voltage of thegate voltage output terminal OUT to the first low voltage Vss1 accordingto the carry signal CR of the next stage. The control terminal of thethird transistor T3 is connected to the node I. The input terminal ofthe third transistor T3 is connected to the gate voltage output terminalOUT, and the output terminal of the third transistor T3 is connected tothe first voltage input terminal Vin1. The third transistor T3 changesthe voltage of the gate voltage output terminal OUT to the first lowvoltage Vss1 according to the voltage of the node I. The controlterminal of the eleventh transistor T11 is connected to the node I. Theinput terminal of the eleventh transistor T11 is connected to the carrysignal output terminal CRout, and the output terminal of the eleventhtransistor T11 is connected to the second voltage input terminal Vin2.The eleventh transistor T11 changes the voltage of the carry signaloutput terminal CRout to the second low voltage Vss2 according to thevoltage of the node I. The control terminal of the eleventh-1 transistorT11-1 is connected to the fourth input terminal IN4. The input terminalof the eleventh-1 transistor T11-1 is connected to the gate voltageoutput terminal OUT, and the output terminal of the eleventh-1transistor T11-1 is connected to the first voltage input terminal Vin1.The eleventh-1 transistor T11-1 changes the gate voltage to the firstlow voltage Vss1 when the inverter output signal of the previous stageis applied with the high voltage. The control terminal of theseventeenth transistor T17 is connected to the second input terminalIN2. The input terminal of the seventeenth transistor T17 is connectedto the carry signal output terminal CRout, and the output terminal ofthe seventeenth transistor T17 is connected to the third voltage inputterminal Vin3. The seventeenth transistor T17 changes the voltage of thecarry signal output terminal CRout to the third low voltage Vss3 basedon the next stage carry signal CR.

In the example of FIG. 17, the first low voltage Vss1 is −5 V, thesecond low voltage Vss2 is −10 V, and the third low voltage Vss3 is −15V. The voltage of the clock signal is between 15 V and −10 V.

The Vgs voltage is the voltage difference between the source and thegate of each transistor of the Q node stabilization unit 514. When thegate-on voltage is output, the Vgs of the fourth transistor T4 is 0 V,the Vgs of the ninth and ninth-1 transistors T9 and T9-1 is −5 V, andthe Vgs of the tenth and tenth-1 transistors T10 and T10-1 is 0 V. Also,the Vgs of the eighth transistor T8 connected to the output terminal inthe inverter unit 512 is −5 V.

As shown above, the Vgs voltages of the fourth transistor T4, the ninthand ninth-1 transistors T9 and T9-1 and the tenth and tenth-1transistors T10 have a value of equal to or less than 0 V, so as togenerate and output the gate-on voltage in the corresponding stage.Since there is no increase in the leakage current, the voltage of thenode Q may be maintained at a constant. As a result, the voltage of thenode Q is stabilized.

In the example of FIG. 17, since the lowest applied voltage is −10 V,either amorphous silicon or oxide semiconductor may be used as thechannel material in the transistors of FIG. 17.

Depending on the level of the applied voltages, the above-describedembodiments may use amorphous silicon or an oxide semiconductor (such asIGZO) as the channel material in the transistors. As mentionedpreviously, when the lowest applied voltage is greater than −10 V,either amorphous silicon or oxide semiconductor may be used as thechannel material in the transistors. However, if the lowest appliedvoltage is less than −10 V, the oxide semiconductor is then used as thechannel material in the transistors.

While this inventive concept has been described in connection with whatis presently considered to be practical exemplary embodiments, it is tobe understood that the inventive concept is not limited to the disclosedembodiments, but further includes various modifications and equivalentarrangements within the spirit and scope of the present disclosure.

What is claimed is:
 1. A display panel comprising: a display areacomprising a gate line and a data line; and a gate driver connected to aterminal of the gate line, wherein the gate driver comprises a pluralityof stages that are integrated on a substrate, and each stage comprisesan inverter unit, an output unit, and a Q node stabilization unit, theoutput unit comprising a first transistor and a first capacitor, whereinthe first transistor includes an input terminal for receiving a clocksignal, a control terminal connected to a node Q and an output terminalconnected to a gate voltage output terminal to output a gate voltage,and a Vgs voltage of a transistor in the Q node stabilization unit has avalue of equal to or less than 0 V when the output unit outputs agate-on voltage.
 2. The display panel of claim 1, wherein a channel ofthe first transistor comprises an oxide semiconductor or an amorphoussemiconductor, and when a voltage applied to each stage is more than −10V, either the amorphous semiconductor or the oxide semiconductor is usedto form the channel of the first transistor, and when the voltageapplied to each stage is less than −10 V, the oxide semiconductor isused to form the channel of the first transistor.
 3. The display panelof claim 2, wherein the output unit is configured to output the gatevoltage at a first low voltage, and the inverter unit is configured tooutput voltage at a second low voltage, wherein the second low voltagehas a lower voltage level than the first low voltage.
 4. The displaypanel of claim 3, wherein each stage further comprises a carry signalgenerator configured to generate and output a carry signal at a thirdlow voltage, wherein the third low voltage has a lower voltage levelthan the second low voltage.
 5. The display panel of claim 4, whereinthe Q node stabilization unit comprises: a fourth transistor comprisingan input terminal and a control terminal for receiving a carry signal ofa previous stage through a first input terminal, and an output terminalconnected to the node Q; a sixth transistor comprising a controlterminal for receiving a carry signal of a second next stage through athird input terminal, an input terminal connected to the node Q, and anoutput terminal for receiving the second low voltage; a ninth transistorcomprising a control terminal for receiving a carry signal of a nextstage through a second input terminal, an input terminal connected tothe node Q, and an output terminal for receiving the second low voltage;and a tenth transistor comprising a control terminal connected to a nodeI wherein the node I corresponds to an output of the inverter unit, aninput terminal connected to the node Q, and an output terminal forreceiving the second low voltage.
 6. The display panel of claim 4,wherein the Q node stabilization unit comprises: a fourth transistorcomprising an input terminal and a control terminal for receiving acarry signal of a previous stage through a first input terminal, and anoutput terminal connected to the node Q; a sixth transistor comprising acontrol terminal for receiving a carry signal of a second next stagethrough a third input terminal, an input terminal connected to the nodeQ, and an output terminal for receiving the third low voltage; a ninthtransistor comprising a control terminal for receiving a carry signal ofa next stage through a second input terminal, an input terminalconnected to the node Q, and an output terminal for receiving the thirdlow voltage; and a tenth transistor comprising a control terminalconnected to a node I as an output of the inverter unit, an inputterminal connected to the node Q, and an output terminal for receivingthe second low voltage.